Communication systems are well known and consist of many types including land mobile radio, cellular radiotelephone, personal communication systems, and other communication system types. Within a communication system, transmissions are conducted between a transmitting device and a receiving device over a communication resource, commonly referred to as a communication channel. To date, the transmissions have typically consisted of voice signals. More recently however, it has been proposed to carry other forms of signals, including data signals. For ease of operation, it is preferable to have the data transmission capability overlay the existing voice communication capability, such that its operation is essentially transparent to the voice communication system while still utilizing the communication resources and other infrastructure of the voice communication system.
In cellular communication systems remote units typically transfer communications between base stations. More particularly, as a remote unit moves to the periphery of a serving base station's coverage area, a handoff is made to a base station that can better serve the remote unit. In addition to transferring communication from one base station to another, often times the handoff between base stations also requires a transferring of communications between two Centralized Base Station Controllers (CBSCs). Currently, such inter-CBSC (hard) handoff results in an adverse radio-link condition where the channel is lost for a short period of time. For a typical "voice" call, the callers perceive the lost channel as a brief muting of their conversation, however, for data transmissions the lost channel may result in the data transmission being aborted, or at a minimum, the retraining of modems to re-establish communication (which can take up to 20 seconds). Therefore, a need exists for a method and apparatus for data transmission within a communication system during adverse radio-link conditions that allows for data transmission without the above-mentioned problems existing with prior-art data transmission schemes.